Authentication Apparatus and Method for Clustering and Authenticating Users

1. An authentication apparatus comprising: a processor operatively coupled to a memory, the processor being programmed to: acquire a plurality of pieces of different context information on a plurality of users, including a target user, which is a target for authentication; perform a first clustering by clustering groups of users of the plurality of users into a plurality of cluster groups based on information related to the plurality of cluster groups, each of the plurality of cluster groups being formed based on the plurality of different context information related to the groups of users of the plurality of users; perform a second clustering by specifying and clustering sub-sets of the plurality of users from each of the plurality of cluster groups of users to form a plurality of belonging clusters of users, one of the plurality of belonging clusters including the target user, the second clustering performed in each of the plurality of cluster groups being performed on a candidate user group of the plurality of users that becomes a candidate for authentication based on a type related to an element included in the context information and based on the acquired context information on the target user; perform a third clustering by specifying and clustering a plurality of candidate users that satisfy a predetermined condition from the plurality of belonging clusters, each of the plurality of candidate users being from a respective partial candidate user group of each of the specified belonging clusters, each candidate user of the plurality of candidate users being specified based on (i) applying a classification model to specify a predetermined candidate user in the partial candidate user group of the specified belonging cluster, and (ii) the acquired context information on the target user; and authenticate the target user based on information related to the specified candidate user associated with each of the plurality of the cluster groups.

2. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify the belonging cluster that is the cluster to which the target user belongs in each of the plurality of the cluster groups based on the information related to the plurality of the cluster groups each of which is based on a different type.

3. The authentication apparatus according to claim 1 , wherein in accordance with the element associated with each of the plurality of cluster groups, the processor is programmed to specify the belonging cluster that is the cluster to which the target user belongs in each of the plurality of the cluster groups based on the plurality of cluster groups in each of which a number of clusters included in each of the plurality of cluster groups is determined.

4. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify a number of clusters in each of the plurality of cluster groups in accordance with the element associated with each of the plurality of cluster groups.

5. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify a candidate user that satisfies a predetermined condition of a classification score that is output by the classification model associated with the belonging cluster in one of the plurality of cluster groups, as a candidate user associated with the one of the plurality of cluster groups.

6. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify a plurality of candidate users that satisfy a predetermined condition of a classification score that is output by the classification model associated with the belonging cluster in one of the plurality of cluster groups, as candidate users associated with the one of the plurality of cluster groups.

7. The authentication apparatus according to claim 1 , wherein the processor is programmed to change a number of the candidate users to be specified in each of the cluster groups in accordance with a number of the plurality of cluster groups.

8. The authentication apparatus according to claim 1 , wherein the processor is programmed to authenticate the target user based on a frequency of appearance of each of the candidate users from among the candidate users associated with each of the plurality of cluster groups.

9. The authentication apparatus according to claim 1 , wherein the processor is programmed to authenticate the target user as a most frequently appearing candidate user from among the candidate users associated with each of the plurality of cluster groups.

10. The authentication apparatus according to claim 1 , wherein the processor is programmed to authenticate the target user based on a predetermined score that is associated with the candidate user associated with each of the plurality of cluster groups.

11. The authentication apparatus according to claim 1 , wherein the processor is programmed to authenticate the target user as a candidate user having a maximum predetermined score from among the candidate users associated with each of the plurality of cluster groups.

12. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify the belonging cluster that is the cluster to which the target user belongs in each of the plurality of cluster groups based on the information related to the plurality of the cluster groups that include the cluster group in which clustering is performed on the candidate user group based on the type related to an attribute of a user.

13. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify the belonging cluster that is the cluster to which the target user belongs in each of the plurality of cluster groups based on the information related to the plurality of the cluster groups that include the cluster group in which clustering is performed on the candidate user group based on the type related to an action history of the user.

14. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify the belonging cluster that is the cluster to which the target user belongs in each of the plurality of cluster groups based on the information related to the plurality of the cluster groups that include the cluster group in which clustering is performed on the candidate user group based on the type related to a terminal device used by the user.

15. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify the belonging cluster that is the cluster to which the target user belongs in each of the plurality of cluster groups based on the information related to the plurality of the cluster groups that include the cluster group in which clustering is performed on the candidate user group based on the type related to a communication environment of the user.

16. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify the target user from the candidate users for each of the belonging clusters associated with each of the plurality of cluster groups based on the classification model that includes a plurality of judgment models associated with each of the users in the partial candidate user group that belongs to the specified belonging cluster.

17. The authentication apparatus according to claim 1 , wherein the processor is programmed to specify the target user from the candidate users for each of the belonging clusters associated with each of the plurality of cluster groups based on the classification model that is a multi-class classification model of the partial candidate user group that belongs to the specified belonging cluster.

18. An authentication method performed by a computer comprising: acquiring a plurality of pieces of different context information on a plurality of users, including a target user, which is a target for authentication; performing a first clustering by clustering groups of users of the plurality of users into a plurality of cluster groups based on information related to the plurality of cluster groups, each of the plurality of cluster groups being formed based on the plurality of different context information related to the groups of users of the plurality of users; performing a second clustering by specifying and clustering sub-sets of the plurality of users from each of the plurality of cluster groups of users to form a plurality of belonging clusters of users, one of the plurality of belonging clusters including the target user, the second clustering performed in each of the plurality of cluster groups being performed on a candidate user group of the plurality of users that becomes a candidate for authentication based on a type related to an element included in the context information and based on the acquired context information on the target user; performing a third clustering by specifying and clustering a plurality of candidate users that satisfy a predetermined condition from the plurality of belonging clusters, each of the plurality of candidate users being from a respective partial candidate user group of each of the specified belonging clusters, each candidate user of the plurality of candidate users being specified based on (i) applying a classification model to specify a predetermined candidate user in the partial candidate user group of the specified belonging cluster, and (ii) the acquired context information on the target user; and authenticating the target user based on information related to the specified candidate user associated with each of the plurality of the cluster groups.

19. A non-transitory computer-readable recording medium having stored therein an authentication program that causes a computer to execute a process comprising: acquiring a plurality of pieces of different context information on a plurality of users, including a target user, which is a target for authentication; performing a first clustering by clustering groups of users of the plurality of users into a plurality of cluster groups based on information related to the plurality of cluster groups, each of the plurality of cluster groups being formed based on the plurality of different context information related to the groups of users of the plurality of users; performing a second clustering by specifying and clustering sub-sets of the plurality of users from each of the plurality of cluster groups of users to form a plurality of belonging clusters of users, one of the plurality of belonging clusters including the target user, the second clustering performed in each of the plurality of cluster groups being performed on a candidate user group of the plurality of users that becomes a candidate for authentication based on a type related to an element included in the context information and based on the acquired context information on the target user; performing a third clustering by specifying and clustering a plurality of candidate users that satisfy a predetermined condition from the plurality of belonging clusters, each of the plurality of candidate users being from a respective partial candidate user group of each of the specified belonging clusters, each candidate user of the plurality of candidate users being specified based on (i) applying a classification model to specify a predetermined candidate user in the partial candidate user group of the specified belonging cluster, and (ii) the acquired context information on the target user; and authenticating the target user based on information related to the specified candidate user associated with each of the plurality of the cluster groups.